Generally, in a blow molding process, a parison is extruded in a size and of an amount of material sufficient to create a desired part. The parison is placed into an open mold in which a blow pin may be oriented, and the mold is closed around the parison. Portions of the parison are pinched between halves of the mold as the mold is closed, and the parison is preferably received around the blow pin. A gas under pressure, such as air, is introduced into the interior of the parison through the blow pin to outwardly expand the parison into the mold and conform the parison to the shape of the mold cavity.
After the blowing procedure, the blow pin may be retracted from the mold and the molded part removed from the mold. Flashing is removed from the molded port at a trimming station, and other secondary finishing operations may be performed. A hole in the molded part where the blow pin was received is then closed with a plug or cover welded to the tank. A cover or plug welded over or in the opening may result in a gap in a barrier layer of the fuel tank thereby allowing increased emissions from the fuel tank. Also, there is a potential for failure in attaching the cover or plug to the fuel tank resulting in an increased scrap rate of fuel tanks produced by a blow molding operation.